A fuel cell is a novel electric power production system that directly converts chemical energy generated by the electrochemical reaction between fuel (hydrogen or methanol) and an oxidizing agent (oxygen or air) into electrical energy. The fuel cell has attracted considerable attention as a next-generation energy source by virtue of the high energy efficiency and the low contaminant discharge, i.e., the environmentally friendly characteristics, and much research on the fuel cell has been carried out.
Based on the kinds of electrolytes used, fuel cells are classified into a phosphoric acid fuel cell, an alkaline fuel cell, a polymer electrolyte fuel cell, a molten carbonate fuel cell, and a solid oxide fuel cell. Among them, the proton exchange membrane fuel cell is classified as a proton exchange membrane fuel cell using hydrogen gas as fuel or a direct methanol fuel cell in which liquid-phase methanol, as direct fuel, is supplied to an anode.
The polymer electrolyte fuel cell is in the spotlight as a portable power supply unit, a power supply unit for vehicles, or a power supply unit for home use by virtue of low operating temperature of 100° C. or less, elimination of leakage problems due to the use of a solid electrolyte, rapid starting and response characteristics, and excellent durability. Especially, the direct methanol fuel cell has a simple fuel supply system, and the overall structure of the direct methanol fuel cell is not complicated as compared to other fuel cells. Furthermore, the miniaturization of the direct methanol fuel cell is possible. Consequently, research on the direct methanol fuel cell as a portable fuel cell is in progress.
FIG. 1 is a typical view illustrating a general direct methanol fuel cell system.
Referring to FIG. 1, the fuel cell system 100 comprises: a fuel cell having a cathode 112 and an anode 114 disposed at opposite sides of an electrolyte membrane 116 made of a polymer material; a first pump 140 for supplying air, including oxygen, as fuel, to the cathode 112; a second pump 150 for supplying a methanol solution, as fuel, to the anode 114; a water controller system 200 constructed such that water, carbon dioxide, and unreacted methanol generated from the fuel cell 110 are introduced into the water controller system 200 through pipes 160 and 170, the carbon dioxide is discharged out of the water controller system 200 through an outlet pipe 190, and the water and the unreacted methanol are supplied again to the fuel cell 110 by the second pump 150; a third pump 180 for supplying the wasted methanol to the water controller system 200; a heat exchanger; and a methanol tank (Pure MeOH).
The methanol solution supplied to the anode 114 is separated into hydrogen ions and electrons. The hydrogen ions move to the cathode 112 through the electrolyte membrane 116, and the electrons moves to the cathode 112 via an external circuit (not shown, whereby electric power is produced from the fuel cell 110. At this time, water is generated from the cathode 112, and carbon dioxide and unreacted methanol are generated from the anode 114. The water, the carbon dioxide, and the unreacted methanol are introduced into the water controller system 200. Among them, the water and the unreacted methanol are mixed with pure methanol, which is supplied from the outside so as to supplement the amount of methanol consumed, and the mixture is supplied again to the fuel cell.
As described above, the direct methanol fuel cell system is normally operated only when a methanol solution is continuously supplied to the direct methanol fuel cell system, and carbon dioxide is continuously removed, which is unlike chemical cells. For this reason, the function of the water controller system, which continuously supplies the methanol solution to the direct methanol fuel cell system, and continuously removes the carbon dioxide, is very important.
Generally, a carbon dioxide discharge position, from which the carbon dioxide, which is gas, is discharged, and a methanol solution discharge position, from which the methanol solution, which is liquid, is discharged, are fixed in the water controller system. As a result, when the water controller system is inclined or shaken, the above-mentioned materials may not be discharged from the corresponding discharge positions.
In order to solve the above-described problems, there has been proposed a method of disposing a liquid separating membrane and an absorbing member for absorbing a methanol solution in the water controller system, thereby reusing the methanol solution absorbed into the absorbing member, which is disclosed in U.S. Unexamined Patent Publication No. 2004-115606, Japanese Unexamined Patent Publication No. 2004-186151, and Korean Unexamined Patent Publication No. 2004-45312. However, the above conventional method has problems in that, when the absorbing member is completely wetted by the methanol solution, the methanol is not absorbed into the absorbing member any more, the carbon dioxide flows in the water controller system, and high pump pressure is needed to resupply the absorbed methanol solution.
On the other hand, Japanese Unexamined Patent Publication No. 2003-163021 discloses a structure constructed such that discharge and supply are accomplished by using a float pipe even when the water controller system is inclined. In this conventional structure, however, an additional unit, which is separated from the water controller system, must be provided, whereby the total size of the fuel cell system is increased.